There is known an in-vehicle electronic control unit including a circuit board and a resin member. The circuit board is equipped with a power supply circuit for performing voltage conversion and mounted with a coil constituting the power supply circuit. The resin member covers the circuit board to protect the circuit board. The resin member is a case which is pre-formed or a molded resin body which is formed to seal the circuit board. Via a bracket fixed to the resin member, the in-vehicle electronic control unit of this kind is attached to a vehicle.
In this in-vehicle electronic control unit, because the circuit board is covered with the resin member, AM band radiation noise generated by the coil is radiated to an outside of the in-vehicle electronic control unit and may be superimposed on an AM radio signal. That is, the radiation noise is superimposed on a radio of the vehicle.
JP2002-9478A corresponding to US2001/0053070A discloses a structure in which electronic parts mounted on a circuit board are covered with an electromagnetic wave shield plate made of metal. When this structure is employed, the level of radiation noise radiated to the outside can be reduced while the circuit board is covered with a resin member.
However, when the structure described in JP2002-9478A corresponding to US2001/0053070A is employed, the number of parts of the in-vehicle electronic control unit increases.
Incidentally, it is conceivable to reduce the level of radiation noise radiated to the outside by employing a metal case in place of the resin member. However, this increases the weight of the in-vehicle electronic control unit and increases the cost.